This invention relates to the field of disk drives designed for use with diskettes (floppy disks), and particularly to techniques for checking the alignment and performance of such disk drives.
Disk drives are known which are designed for use with flexible recording media popularly known as diskettes or floppy disks. Generally, such disk drives include a motor driven drive spindle and associated clamping mechanism for receiving and rotating a floppy disk at a predetermined constant speed, a transducer positioning assembly for radially positioning a read/write transducer in response to track position commands, and electronic circuitry for operating the motor, the transducer positioning mechanism and also for furnishing data to and reading data from the floppy disk. Some disk drives are designed with only one read/write transducer, while others are designed with a pair of such transducers for enabling data to be written on to and read from both sides of the floppy disk.
Data is organized on a floppy disk using a series of ideally concentric tracks, with each track being divided into a plurality of sectors formatted in a predetermined standard manner, such as an IBM 3740 format or an IBM System 34 format. The format specifies the sequence and location of certain types of information, such as track number, sector number, data field, etc. Floppy disk recording capacity is also specified as the number of tracks per inch, with forty-eight tracks per inch and ninety-six tracks per inch being popular recording densities, the former requiring a track width in the radial direction of 12 mils., the latter requiring a track width of 6 mils. The actual data is recorded onto a track using conventional magnetic recording techniques for binary data.
In order to reliably store and retrieve data on a diskette, certain mechanical parameters must be observed. For example, whenever the read/write transducer is positioned to a given track, the positioner mechanism should ideally locate the transducer symmetrically over the center line of the circular data track, with the transducer gap perpendicular to the track center line (zero Azimuth). In addition, as the transducer is moved from track to track, such movement should ideally be precisely along a radius of the diskette and not skewed at an angle to the radius (zero skew). Further, as the transducer is moved to the same track radially inwardly and radially outwardly, the final position over the track should be the same (zero hysteresis). In addition to these parameters having to do with the transducer positioning mechanism, other parameters are also critical to the proper performance of the disk drive. For example, the angular rotational position of the floppy disk must be precisely known to insure that data is stored or retrieved at a particular location in a given sector of a particular track: for this reason, each floppy disk is provided with an index hole as a zero angle reference, and the passage of this hole past an index transducer mounted in the disk drive acts as a zero reference point. Misalignment of the index transducer in the disk drive can cause erroneous data storage and retrieval. In addition, since the data is recorded in ideally concentric tracks on the floppy disk, any eccentricity of the disk drive spindle/clamp assembly will cause read and write errors.
In order to analyze the above noted disk drive alignment and performance characteristics, special alignment diskettes have been designed which contain prerecorded information in preselected track locations. Generally, three different types of prerecorded data have been used as such a diagnostic aid: alternate offset tracks, progressively offset tracks and Azimuth tracks. An alternate offset track is usually arranged as a sector identification number followed by a sector data field offset either radially inwardly or radially outwardly by a predetermined distance. The offset sector data field is followed by the next sector identification number and another sector data field offset in the opposite radial direction by the same predetermined distance. The sequence continues around the entire track. A progressively offset track is similar to an alternate offset track with the exception that the sector data fields are progressively offset from track center line by an increasing value: thus, for example, in one such implementation, the first two sector data fields are recorded directly on center, the sector three data field is recorded with a four milli-inch offset in the direction of the center of the disk, the sector four data field is recorded with a four milli-inch offset in the direction of the outer periphery of the floppy disk, the sector five data field is recorded with an offset of five milliinches towards the hub, the sector six data field is recorded with a five mili-inch offset in the peripheral direction, etc. The Azimuth track is recorded using the sector ID followed by the sector data field sequence, but with each data field being recorded at an Azimuthal angle with respect to the track center line, with alternate data fields being recorded at positive and negative angles.
In use, the alternate offset track has been employed to check the eccentricity of the disk drive spindle/clamp assembly by determining the readability of a sector, which is influenced by the reduction in amplitude due to the offset: for a perfectly concentric track, the amplitudes should be equal, while for an eccentric track the amplitudes will vary. In known alignment diskettes, a single alternate offset track has been used for checking eccentricity. The progressively offset tracks have been used to measure the radial alignment and hysteresis of the disk drive positioner mechanism: the former is checked by monitoring the electrical output signal to determine the point at which the sector data field is so far displaced from the track center line that the signals fall below the acceptable readability level. If the disk drive is aligned properly, the first two sectors for which a read failure is observed should be equally displaced on either side of track center line, while a misaligned disk drive is signified by a nonsymmetrical maximum read pattern. The latter is checked by first positioning the transducer to the progressive alignment track by approaching the track along a first direction, followed by positioning the transducer to the same track from the opposite radial direction: the difference in the two radial alignments signifies the drive hysteresis error. The Azimuth track is used to check the head Azimuth alignment in a manner similar to the use of the progressive offset tracks to check radial alignment: for a perfectly aligned drive, the read/write transducer will fail to read sectors that are equally rotated clockwise and counterclockwise, while a misaligned head will produce nonsymmetrical maximum read patterns.
In addition to the above described prerecorded alignment tracks, known alignment diskettes have been provided with timing tracks consisting of circumferential data bits precisely placed on the track relative to the photo index pulse to measure alignment of the index transducer and rotational speed.
Diagnostic diskettes of the above type have been found useful in measuring disk drive alignment and performance for a number of reasons. Firstly, the variety of tests noted above can be performed in a relatively short period of time, on the order of five minutes, under actual disk drive operating conditions. Since the tests are performed using software routines incorporated into the associated computer with which the disk drive under test is actually employed, no special equipment is required, and thus no special technical training is necessary (provided that the user understands the operation of his own computer). Further, since the diagnostic diskette has the same physical characteristics as an ordinary user diskette, any errors due to unusual environmental temperature and humidity conditions in the environment of the disk drive will be exhibited by errors in the alignment performance.